Transcript Glaucoma - pgblaster

Glaucoma
Prithwiraj Maiti
R.G.Kar Medical College
What is Glaucoma?
• Glaucoma is a chronic, progressive optic
neuropathy caused by a group of ocular
conditions which ultimately lead to damage
to the optic nerve and loss of visual function.
Risk factor of Glaucoma
• The most common risk factor for development
of glaucoma is a high intraocular pressure
(IOP).
• There may be 2 causes of rise in IOP:
a. Increased production of aqueous humour.
b. Decreased excretion of aqueous humour.
Pathways of Exit
• The excretion of aqueous occurs through 2
different pathways:
a. Through the trabecular meshwork, situated
in the angle of anterior chamber [Trabecular
outflow] : Major pathway.
b. Through the ciliary body [Uveo-scleral
outflow]: Minor pathway.
Pathways of Aqueous Exit
Site of Obstruction To Aqueous Flow
• It is clear from the previous discussions that
there may be obstruction to the aqueous flow
in 2 positions:
1. Through the pupil.
2. Through the trabecular meshwork.
Pathogenesis of Glaucoma
• Wherever the obstruction is, the final
outcome is an increase in IOP, which has
some bad consequences:
a. The eye can withstand a high IOP for its
protective coverings. But at the lamina
cibrosa region, where the optic nerve enters
into the eye, this can’t happen due to poor
protective coverings.
Raised IOP
Mechanical pressure at Lamina
Cibrosa
A decrease in axoplasmic flow
Ischemia of optic nerve head
Apoptosis (Death of ganglion
cells)
b. The second mechanism of optic nerve damage is
vascular compression.
Raised IOP
Mechanical compression of
vessels at Lamina Cibrosa
Decreased nutrition to the
optic nerve head
Apoptosis (Death of
ganglion cells)
Diagnosis of Glaucoma (dG)
• The diagnosis of Glaucoma is made after
looking for a combination of clinical signs:
1. A rise in IOP.
2. Changes in the optic nerve head.
3. Changes in the visual field.
dG: Rise in IOP
• A diurnal variation in the IOP of > 6-8 mm Hg
should always be investigated for Glaucoma
even in the presence of a normal IOP (~20 mm
Hg).
• A single reading is useless, but periodic check
up to detect baseline IOP and normal variation
is important in diagnostic and curative
purpose in Glaucoma.
dG: Change in Optic Nerve Head
• The following changes are commonly seen in
Glaucoma:
1. An enlarged CUP: DISC ratio (>0.5).
2. Assymetry in CUP: DISC ratio between 2 eyes
(>0.2).
3. Thinning and pallor of neuroretinal rim.
4. Superficial disc hemorrhage.
5. Vascular signs (Baring of circumlinear vessels:
BCLV).
6. Parapapillary atrophy.
In Glaucoma
Normal
Superficial Disc Hemorrhage In
Glaucoma
Baring of Circum Linear Vessels [BCLV]
This vessel was
originally at the
rim but is now
hanging out in
space.
It is a sign of
GLAUCOMA and
indication of
Progressive
cupping.
Parapapillary atrophy
Parapapillary atrophy has
been defined as atrophic
abnormalities in the
layers of the retinal
pigment epithelium,
photoreceptors and
chorio-capillaris.
dG: Change In Visual Field: Scotoma
Scotoma is an area of
partial alteration in the field
of vision consisting of a
partially diminished/
entirely degenerated visual
acuity that is surrounded by
a field of normal/ relatively
well-preserved vision.
Scotoma in Glaucoma
Some of common types of Scotoma associated with Glaucoma:
Relative paracentral scotoma
Nasal step
Siedel scotoma
Arcuate scotoma
Double arcuate/ Ring scotoma
End stage/ near-total field defect.
Relative Paracentral Scotoma
There are areas where
smaller/ dimmer
targets are not seen but
larger/ brighter targets
are seen.
Nasal step
Appearance of a
horizontal shelf in
the nasal visual
field.
Siedel Scotoma
Start at poles of blind
spot, arching over the
macular area without
reaching the horizontal
meridian nasally.
Arcuate scotoma
Start at superior
pole, arching over
macular area, never
crossing horizontal
meridian.
Double arcuate/ Ring Scotoma
Only central and temporal vision are left.
End Stage/ Near Total Field Defect
Classification of Glaucoma
Glaucoma
Congenital
glaucoma
Primary adult
glaucoma
Open angle
Secondary
glaucoma
Angle closure
Primary Open Angle Glaucoma
Diagnosis of POAG
• At least 2 of the 3 clinical signs should be
present to diagnose POAG in the presence of
a normal, open angle confirmed by
gonioscopy:
1. An IOP> 21 mm Hg on >1 occasion and a
diurnal variation of >8 mm Hg.
2. The presence of suggestive optic nerve head
changes.
3. Visual field defects.
Primary Angle Closure Glaucoma
Diagnostic Techniques Used In Glaucoma
• There are 2 important diagnostic tools for
glaucoma:
1. Gonioscopy: To view the angle of Anterior
Chamber.
2. Goldmann’s Applanation Tonometry: To
measure the intraocular pressure (IOP).
Diagnostic Technique 1: Gonioscopy
• Gonioscopy is a method to gain a view of
angle of AC with the help of a goniolens and a
slit lamp/ operating microscope.
• In the Indirect Gonioscopy method, a contact
lens is inserted between the lids to lie upon
the anaesthetized cornea; fitted with a mirror
placed at an angle of 62°-64°, in which the
image of the recess of AC is reflected.
Indirect Gonioscopy
• In the Direct Gonioscopy method, a dome
shaped glass contact lens refracts light from
angle of AC directly into observer’s eye (without
any mirror); thus providing a much clearer view
of the angle.
• In the Indentation Gonioscopy method, the
aqueous is displaced from the centre to the
periphery so that iris is pushed backwards at the
angle. It allows visualization of the angle of AC in
case of a narrow angle [as in PACG].
Normal Angle Structures Seen In
Gonioscopy
Diagnostic Technique 2:
Goldmann’s Applanation Tonometry: Basics
• Applanation tonometry measures IOP by
providing force which flattens the cornea.
• It is based on Imbert-Fick law:
Pressure within a sphere (P) is roughly equal
to the external force (f) needed to flatten a
portion of the sphere divided by the area (A)
of the sphere which is flattened: P = f / A.
• But this law applies to a perfect sphere (dry
and thin walled) only.
Continued…..
• However, the human eye is not thin walled
and it is not dry, producing two confounding
forces:
(1) A force produced by the eye’s scleral rigidity
(because the eye is not thin walled), directed
away from the globe; and
(2) A force produced by the surface tension of
the tear film (because the eye is not dry),
directed toward the globe.
A) When a flat surface is applied to the cornea with enough force (w) to
produce a circular area of flattening greater than 3.06mm in diameter,
the force caused by scleral rigidity (r) is greater than that caused by the
tear film surface tension (s).
(B) When the force of the flat surface produces a circular area of
flattening exactly 3.06mm in diameter, the confounding forces caused by
scleral rigidity and tear film surface tension cancel each other. The
applied force (w) then becomes directly proportional to the intraocular
pressure (p).
How does the observer know when the area of
applanation is exactly 3.06mm in diameter so that
the intraocular pressure can be measured?
• The applanation tonometer is mounted on a
biomicroscope to produce a magnified image.
• When the cornea is applanated, the tear film,
which rims the circular area of applanated
cornea, appears as a circle to the observer.
• The tear film often is stained with fluorescein dye
and viewed under a cobalt-blue light in order to
enhance the visibility of the tear film ring.
• The clinician looks through the applanation head
and adjusts the pressure until the half circles just
overlap one another.
• At this point, the circle is exactly 3.06mm in
diameter, and the reading on the tonometer
(multiplied by a factor of 10) represents the
intraocular pressure in millimeters of mercury.
Types of PACG
• PACG is of 3 different types:
1. Acute,
2. Subacute,
3. Chronic.
• In acute PACG, there is sudden occlusion of
the angle of AC and explosive rise in IOP with
severe unilateral headache, diminution of
vision and a red eye.
• In subacute PACG, in a person with a shallow
AC, some stress factors like watching TV for a
long time/ rapid eye movement during sleep
etc. causes a sharp rise in IOP with severe
unilateral headache/ coloured halos/ blurring
of vision.
• Repeated subacute attacks of PACG leads to
chronically elevated IOP and synechial closure;
often designated as “Chronic PACG”.
Treatment Of Glaucoma
• Line of treatment:
1. Remove precipitating factors (any drug that may elevate
IOP, i.e., steroids etc.).
2. IOP Reduction by:
a. Medication(s),
b. Laser,
c. Surgery.
3. Correct the angle closure by:
a. Laser,
b. Surgery.
4. For secondary glaucoma, treat the underlying pathology.
Medication(s)
LASER: POAG
• Laser therapy of POAG consists of laser
trabeculoplasty.
• In this procedure, laser spots are applied
gonioscopically to coagulate the trabecular meshwork;
increasing the space available for aqueous excretion.
• Lasers commonly used: Argon diode/ frequency
doubled Nd-YAG laser.
• 50-100 laser spots, each of 50 µM size are applied at
the junction of ant. and post. trabecular meshwork.
• The immediate incidence is a transient rise in the IOP,
which requires prophylactic treatment with Topical
Apraclonidine.
LASER: PACG
• In case of PACG, the IOP is immediately controlled
by using i.v. acetazolamide 500 mg +/ i.v.
mannitol; then topical pilocarpine 2% is instilled
to constrict the pupil.
• After the IOP is controlled, a laser iridotomy is
mandatory in all eyes in any form of PACG and
also prophylactically in the fellow unaffected
eye.
• Postoperatively, steroids and antiglaucoma
medications are required for 5-7 days to prevent
a rise in the IOP and to control any inflammation.
Surgery: Trabeculectomy
• Surgery is undertaken only when the
conventional medical therapy fails to arrest
visual field loss/ in a patient who can’t be
followed up closely/ a patient who has a very
high IOP which is uncontrollable to
medications alone.
• The preferred surgical treatment is
trabeculectomy, gold standard for glaucoma
surgeries
Indications of trabeculectomy
1. IOP too high to prevent future glaucoma
damage and functional visual loss.
2. Documented progression of glaucoma damage
at current level of IOP with treatment.
3. Presumed rapid rate of progression of
glaucoma damage without intervention.
4. Poor compliance with medical therapy: cost,
inconvenience, understanding of disease,
refusal.
5. Intolerance to medical therapy due to side
effects.
Basic of Surgery
Steps of Surgery
• As the steps of surgery are complex and
boring stuff for undergraduates, we are
showing it through a video.
• Here it should be noted that in
trabeculectomy, one of the most important
steps in surgery is the application of
antimetabolite drops (like Mitomycin C/ 5 FU
etc.) to prevent the healing of the drainage
channel to subconjunctival space.
Resources Used:
1. Parson’s Disease Of The Eye.
2. Yanoff’s Ophthalmology.
3. Bassak’s Practical Ophthalmology CD-ROM.
4. Glaucoma Guideline: Asia Pacific.
5. Youtube Videos.